1. Field of the Invention
The present invention relates to an electric power steering apparatus for a vehicle, and more particularly to an electric power steering apparatus for a vehicle, which has a structure in that a motor shaft, an input shaft, a pinion shaft, and the like, are coaxially disposed to improve a structure of a conventional electric power steering in which an electric motor is essentially exposed, so as to prevent interference with the other structures, thereby forming a layout of the electric power steering apparatus to be compact, and in which, although a first ring gear and a second ring gear have different number of gear teeth, identical planetary gears are tooth-engaged with the first and second ring gears, thereby improving convenience for assembling of the planetary gear assembly and obtaining a large gear reduction ratio.
2. Description of the Related Art
FIG. 1 is a view illustrating a structure of a conventional electric power steering apparatus.
As shown in FIG. 1, the conventional electric power steering apparatus 100 for the vehicle includes a steering system extending from a steering wheel 101 to both wheels 108, and an auxiliary power mechanism 120 for supplying an auxiliary steering force to the steering system.
The steering system includes a steering shaft 102, which has one end thereof connected to the steering wheel 101 and the other end thereof connected to a driving shaft by means of a universal joint 103.
The driving shaft includes an input shaft 104 connected to the steering shaft 102, and a pinion shaft 106 connected to the input shaft 104 by means of a torsion bar (not shown), and having a pinion gear 111 mounted on a lower end thereof.
The pinion gear 111 mounted on the pinion shaft 106 is tooth-engaged with a rack gear 112 formed on an outer peripheral surface of a rack bar 109, and the rack bar 109 has both ends connected to wheels 108 of the vehicle through tie rods 151 and knuckle arms 153, respectively.
The auxiliary power mechanism 120 includes a torque sensor 125 for detecting a torque generated at the input shaft 104 as a driver rotates the steering wheel 101 and outputting an electric signal proportional to the detected torque, an electric control unit (ECU) 123 for generating a control signal based on an electric signal transmitted from the torque sensor 125, an electric motor 130 for generating an auxiliary power based on a control signal transferred from the electric control unit 123, and worm 141 and worm wheel 143 for transferring an auxiliary power from the electric motor 130 to the pinion shaft 106.
However, in the conventional electric power steering apparatus for the vehicle, the electric motor, the worm, the worm wheel, and the like, are used to construct a reducer of the auxiliary power mechanism. In this structure, the electric motor is essentially exposed when they are mounted on the vehicle, and causes interference with other structures. Accordingly, there is a disadvantageous in the layout.